Imprinted semiconductor multiplex detection array

ABSTRACT

An array of sensor devices, each sensor including a set of semiconducting nanotraces having a width less than about 100 nm is provided. Method for fabricating the arrays is disclosed, providing a top-down approach for large arrays with multiple copies of the detection device in a single processing step. Nanodimensional sensing elements with precise dimensions and spacing to avoid the influence of electrodes are provided. The arrays may be used for multiplex detection of chemical and biomolecular species. The regular arrays may be combined with parallel synthesis of anchor probe libraries to provide a multiplex diagnostic device. Applications for gas phase sensing, chemical sensing and solution phase biomolecular sensing are disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to active solid state devices,specifically to apparatus and method for making and using sensors withnanodimensional features that are responsive to molecular compounds,organisms or gas molecules.

2. Description of Related Art

The use of nanowires and nanotubes for label-free direct real-timedetection of biomolecule binding is known in the art. Nanowires andnanotubes have the potential for very high-sensitivity detection sincethe depletion or accumulation of charge carriers, which is caused bybinding of a charged biological macromolecules at the surface, canaffect the entire cross-sectional conduction pathway of thesenanostructures. See, e.g., Direct Ultrasensitive Electrical Detection ofDNA and DNA Sequence Variations Using Nanowire Nanosensors, by Jong-inHahm and Charles M. Lieber, Nano Letters, 2004 (Vol. 4, No. 1 pp.51-54), which is incorporated by reference (hereinafter Lieber). Lieberdiscloses measurable conductance changes associated with hybridizationof a Peptide Nucleic Acid (PNA) receptor with complimentary DeoxyriboseNucleic Acid (DNA) target molecule. A practitioner skilled in the artwill appreciate that a Peptide Nucleic Acid (PNA) receptor could besubstituted with a Deoxyribose Nucleic Acid (DNA) receptor or a RiboseNucleic Acid (RNA) receptor.

U.S. Pat. No. 7,301,199 discloses nanowires fabricated using lasercatalytic growth (LCG), and is incorporated by reference in itsentirety. In LCG, a nanoparticle catalyst is used during the growth ofthe nanoscale wire. Laser vaporization of a composite target composed ofa desired material and a catalytic material creates a hot, dense vapor.The vapor condenses into liquid nanoclusters through collision with abuffer gas. Growth begins when the liquid nanoclusters becomesupersaturated with the desired phase and can continue as long asreactant is available. Growth terminates when the nanoscale wire passesout of the hot reaction zone or when the temperature is decreased. InLCG, vapor phase semiconductor reactants required for nanoscale wiregrowth may be produced by laser ablation of solid targets, vapor-phasemolecular species, or the like. To create a single junction within ananoscale wire, the addition of the first reactant may be stopped duringgrowth, and then a second reactant may be introduced for the remainderof the synthesis. Repeated modulation of the reactants during growth isalso contemplated, which may produce nanoscale wire superlattices. LCGalso may require a nanocluster catalyst suitable for growth of thedifferent superlattice components; for example, a gold nanoclustercatalyst can be used in a wide-range of III-V and IV materials. Nearlymonodisperse metal nanoclusters may be used to control the diameter,and, through growth time, the length of various semiconductor nanoscalewires. This method of fabricating nanowires is known in the art, andconstitutes one method of creating nano-scale features.

The use of photolithography for fabrication of micron-scale features iswell known in the art. In “standard” photolithography, multiple stepsare performed to pattern features on a surface. In the initial step, thesurface, which may be a p- or n-doped silicon wafer, is cleaned ofsurface contaminants. Persons skilled in the art will appreciate thatmany planar surfaces can be patterned in this way, including surfaceswith multiple layers, such as a substrate of p- or n-doped silicon, amiddle layer of insulating silicon dioxide (SiO₂), with a top layer ofmetal. Next, adhesion promoters are added to the surface to assist inphotoresist coating. Photoresist may be spin-coated onto the surface,forming a uniform thickness. The wafer containing the photoresist layeris then exposed to heat to drive off solvent present from the coatingprocess. Next, a photomask, which may be made of glass with a chromiumcoating, is prepared. The features desired on the surface of the waferare patterned on the photomask. The photomask is then carefully alignedwith the wafer. The photomask is exposed to light, the transparent areasof the photomask allow light to transfer to the photoresist, thephotoresist reacts to the light, and a latent image is created in thephotoresist. The photoresist may be either positive or negative tonephotoresist. If it is negative tone photoresist, it is photopolymerizedwhere exposed and rendered insoluble to the developer solution. If it ispositive tone photoresist, exposure decomposes a development inhibitorand developer solution only dissolves photoresist in the exposed areas.Simple organic solvents are sufficient to remove undevelopedphotoresist. The techniques of “etch-back” and “lift-off” patterning areused at this stage. If the “etch-back” technique is used, thephotoresist is deposited over the layer to be pattered, the photoresistis patterned, and the unpatterned areas of the layer are removed byetching. If the “lift-off” technique is used, photoresist is depositedfollowed by deposition of a thin film of desired material. Afterexposure, undeveloped photoresist is removed by the developer solventand carries away the material above it into solution leaving behind thepatterned features of the thin film on the surface. Removal of theremaining photoresist may be accomplished through oxygen plasma etching,sometimes called “ashing”, or by wet chemical means using a “piranha”(3:1 H₂SO₄:H₂O₂) solution.

Although widely used and extremely useful as a micron-scale patterningtool, “standard” photolithography is limited in the resolution of thefeatures it can pattern. The ability to project a clear image of a smallfeature onto the wafer is limited by the wavelength of the light that isused, and the ability of the reduction lens system to capture enoughdiffraction orders from the illuminated mask. The minimum feature sizethat a projection system can print is given approximately by:CD=k₁*(λ/NA); where CD is the minimum feature size (also called thecritical dimension, target design rule); k₁ (commonly called k₁ factor)is a coefficient that encapsulates process-related factors, andtypically equals 0.4 for production; λ is the wavelength of light used;and NA is the numerical aperture of the lens as seen from the wafer.According to this equation, minimum feature sizes can be decreased bydecreasing the wavelength, and increasing the numerical aperture, i.e.making lenses larger and bringing them closer to the wafer. However,this design method runs into a competing constraint. In modern systems,the depth of focus (D_(F)) is also a concern: D_(F)=k₂*(λ/(NA)²). Here,k₂ is another process-related coefficient. The depth of focus restrictsthe thickness of the photoresist and the depth of the topography on thewafer. One solution known in the art is utilization of light sourceswith shorter wavelengths (λ), and creation of lenses with higher numericapertures (NA). The drawback to this solution is the increasinglyprohibitive high cost of fabricating complex sources and optics.

Nanoimprint Lithography (NIL) solves the problem of limited minimumfeature sizes and high cost by patterning nano-scale features into aquartz plate, referred to as the “template” that can be applied directlyto the surface of a wafer and transferring the pattern 1:1 into aphotoresist layer. “Step and Flash Imprint Lithography,” by Resnick, D.,et al., Solid State Technology, (2007), Feb. , 39, which is incorporatedin its entirety by reference, discloses the method to pattern nano-scalefeatures by first imprinting the features into a photoresist layer anddry etching the imprint layer into the desired thin film layer on awafer. The S-FIL process, now generally known in the art as NanoimprintLithography (NIL), requires that electron beam lithography be first usedto “write” the desired imprint pattern into the template. The templatemay be a quartz plate substrate coated with a chromium (Cr) layer. Theelectron beam resist is patterned and the pattern is transferred intothe Cr layer and the final three-dimensional relief structure is etchedinto the quartz plate or “template.” After transfer of the pattern intothe quartz layer, the Cr layer is stripped, leaving an opticallytransparent template with the imprint pattern etched onto one surface.

To create the imprint pattern into a thin film layer on a wafersubstrate, a low-viscosity photocurable monomer—known as the etchbarrier—is dispensed on its surface. The transparent template is broughtinto contact with the monomer at a slight angle, creating a monomerwavefront that spreads across the surface and fills the threedimensional relief structures of the transparent template. UV lightphotopolymerizes the monomer and the template is separated from thewafer, leaving a solid replica of the reverse of the template on thesubstrate surface. Post-processing consists of a breakthrough etch ofthe residual layer of the monomer, followed by a selective etch into anorganic layer and finally transfer of the pattern into the desiredlayer; for example a semiconductor thin film. Imprint lithography hasbeen used to create feature CDs on the order of 20 nm in high densityover large areas, e.g. 4-6″ wafers during a single imprint process.

In a similar fashion, the reverse process (S-FIL/R) can be accomplished.This is achieved by imprinting the surface using the template followedby spinning on an organic layer. The organic layer is etched back toexpose the top surface of the silicon-containing imprint which is thenselectively etched to the substrate using the organic layer as an etchstop. A final set of etching conditions is used to transfer the patterninto the substrate material. Nanoimprint Lithography has the advantageof being limited only by physical resolution of the template rather thanbeing limited by wavelength and numeric aperture, as in standardphotolithography. As new methods emerge for template fabrication, acorresponding increase in feature resolution can be expected.

U.S. Pat. No. 6,426,184 discloses a method for massively parallelsynthesis of DNA, RNA, and PNA molecules utilizing photogeneratedreagents (PGR), and is incorporated herein by reference. The methodinvolves a microfluidic chamber comprising a series of wells that act asreaction sites with a transparent sealed cover. Within each well, a“linker” molecule functionalized with a “reactive group” is attached tothe substrate. The reactive group couples a “spacer group” which thencouples the first nucleotide to the surface. The nucleotide bears a“protection group” initial. The reactive precursor to the PGR isintroduced through the microfluidic chamber into the well sites.Selective wells receive light using a spatial light modulating deviceduring a given exposure step which results in a “photogenerated reagent”within each well that was exposed. PGR is activated only in the wellsthat are exposed to light, thereby causing a chemical reaction with theprotection group, and “de-protecting” the terminal nucleotide in thenucleic acid sequence. The PGR is flushed from the system, and a selectnucleotide with a “protection group” is introduced. The nucleotide with“protection group” is covalently bonded to the end of the nucleic acidsequence in the selected wells. In all other wells that do not getexposed to light, no reaction takes place and no nucleotide couplingoccurs during that exposure cycle. After proper washing, oxidation, andcapping steps, the addition of the cycle is repeated in such a fashionto synthesize any combination of nucleotides onto surface-anchorednucleic acid sequences that are specific to each well. The process iscontinued until the oligonucleotides of interest are constructed overthe entire array. The chemistry of building oligonucleotides is wellknown in the art. Because the sequence is known for each well in themultiplex detection array, diagnostic tests that result in a signaltransduction event can be performed by first identifying if a reactionoccurs for a given well, and second by determining the position, andhence identity of the “known” anchor probe sequence.

“Light Directed Massively Parallel On-chip Synthesis of Peptide Arrayswith t-Boc Chemistry,” by Gao, X., et al., Proteomics, (2003), 3, 2135discloses PNA synthesis using t-Boc chemistry, and is incorporated byreference herein. This article is an example of chemical syntheses ofanchor probe libraries known in the art.

What is needed is a cost-effective, time-efficient, reproducible methodfor fabricating arrays of nano-scale features on a single wafer to forma sensor device or a matrix of devices for multiplex detection ofselected analytes using many simultaneous detection zones, by detectingchanges in electrical characteristics of the nano-scale materials foreach device. Method for making such sensors and arrays is needed.

SUMMARY OF INVENTION

The problem of reproducibly fabricating semiconducting active layersthat provide the necessary nano-dimensional features for directelectrical detection in sensing applications is solved using nanoimprintlithography to define groups of semiconducting nanotraces betweenelectrodes. Such groups may be used as a sensor or, when anchored probemolecules are covalently coupled or synthesized to the surfaces, be usedfor multiplex detection of analytes. Nanoimprint lithography alsoprovides a method to fabricate arrays of semiconducting electrode“nanotraces” in a controllable and regular pattern in a singleprocessing step. A method that provides controlled fabrication ofnanophase features provides a means for detection of gases adsorbed onthe semiconductor surfaces or multiplex detection of many simultaneousdetection zones. Binding of complementary targets to the anchored probemolecules in the vicinity of the semiconducting active layer produces achange in electrical conductivity of the semiconducting active layerthat can be monitored externally for each sensor device in the array inparallel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a subset of the multiplex detection array showing sixsensor devices with the imprinted semiconductor nanotraces. The insetshows the features of an individual semiconductor nanotrace in the setof nanotraces disposed between the electrodes.

FIGS. 2 A-F illustrates the fabrication sequence for preparing theelectrical base including the semiconductor nanotraces for the multiplexdetection array.

FIGS. 3 A-E illustrate the process of preparing the imprint pattern forthe semiconductor nanotraces.

FIGS. 4 A-E illustrate the process for etching the semiconductornanotraces.

FIG. 5 shows a high resolution SEM of the imprinted SFIL over thesemiconductor active layer.

FIGS. 6 A-B show a high resolution SEM of the transfer of the imprintpattern to form the semiconductor nanotraces. This image depictsnanotraces with transverse bridging segments.

FIGS. 7 A-C show the multiplex detection device preparation steps forperforming PGR in the preferred embodiment and packaging onto theelectronics board.

FIGS. 8 A-B show examples of the response generated during bindingreactivity in the preferred embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates an overview of a subset of the electrical detectionportion of multiplex detection array 101, which consists of sixindividual sensor devices 102A-F. A single sensor device, e.g. 102A, isdefined as a region that is independently electrically addressable fromneighboring devices 102B-F in FIG. 1. Some of the features have beenremoved in this overview to enable a visual representation of the corecomponents of multiplex detection array 101. Each sensor device 102consists of a set of two interdigitated electrodes including sourceelectrode 103, and drain electrode 104 of an individual sensor, e.g.sensor device 102B. A third gate electrode 105 may be positioned tocross under the interdigitated portion of each column of sensor devices102, e.g. sensor devices 102C and 102F in FIG. 1. Gate electrode 105 isin a lower plane than source 103 and drain 104 electrodes and isseparated by thin oxide dielectric layer 106 supported by a suitablesubstrate wafer 107, for example a silicon wafer or polymeric film. Allof the electrodes 103-5 have relatively large scale features (˜1-5 μm)that are patterned using standard lithography. In this example, gateelectrode 105 is common to each column of sensor devices 102 andterminates at gate electrode bonding pad 108 in an area remote from thesensor devices 102. Similarly, source electrode 103 is common to allsensor devices 102 in each column in the array and terminates at sourceelectrode bonding pad 109 in an area remote from sensor devices 102 andparallel with gate electrode 105. Each of the drain electrodes 104terminates at each sensor device 102 at drain electrode stub bonding pad110. A secondary process enables electrical continuity of drainelectrode stub bonding pad 110 to be transferred to a higher plane thatis separated by oxide insulating layer 111. Electrical continuity istransferred by metal filling of drain electrode vias 112 that arepositioned over each drain electrode stub bonding pad 110 and below eachdrain electrode pick-up pad 113, which is in the higher plane. Theportion of drain electrode 104B in this plane is common for each row ofsensor devices 102; for example, sensor devices 102A-C and sensordevices 102D-F in FIG. 1, and terminates at drain electrode bonding pad114. Drain electrodes 104B are perpendicular to the source 103 and gate105 electrodes but in a different electrode plane to prevent shortingacross the sensor devices 102.

In the center of each sensor device 102 is a set of parallelsemiconductor “nanotraces” 115 that are perpendicular to and disposedacross, the interdigitated finger region of the source 116 and drain 117electrodes. Semiconductor nanotraces 115 can be fabricated usingnanoimprint lithography. Each semiconductor nanotrace 118, FIG. 1 inset,in the set of parallel nanotraces 115 provides a narrow electricalbridge between source 103 and drain 104 electrodes by making contactwith the interdigitated finger region of each of the source 116 anddrain 117 electroces. In the preferred embodiment (FIG. 1 inset), thedimensions of individual nanotraces 118 range between 10 nm to about 100nm in width 119 and depth 120 where the depth 120 is defined by thethickness of the originally deposited semiconducting active layer. Morepreferable, the width of each nanotrace is less than about 50 nm. Mostpreferable, the width of each nanotrace is less than about 20 nm. Pitch121 between neighboring nanotraces 118 in the set of parallel nanotraces115 can vary depending on the number of nanotraces 118 included in theset and the total surface area of the interdigitated finger region ofsource 116 and drain 117 electrodes. The number of nanotraces 118 canrange from one to hundreds depending on the application. The length 122of the semiconductor nanotraces 118 spans the full distance from theoutside source interdigitated finger 116 to the outside draininterdigitated finger 117 of each sensor device 102, crossing over allinterdigitated fingers therebetween.

When an external electric field is applied across drain electrode 103and source electrode 104, electrical current must travel through the setof parallel semiconductor nanotraces 115 to pass from the sourceelectrode finger 116 to the drain electrode finger 117. Because thewidth 119 of each semiconductor nanotrace 118 is on the order of theelectrical diffusion pathway and the surface-to-volume ratio for eachnanotrace 118 is large, the current traveling through each nanotrace 118is highly influenced by its local environment 123 near the surface. Theresponse is proportional to the degree in which the electrical currenttraversing the set of semiconductor nanotraces 115 is influenced bychanges in the electric field strength near the surface of eachnanotrace 118. The local environment 123 can be a gas phase, e.g. an airplenum sampling for toxic gases, a solution environment e.g. and aqueousbuffer sampling for complementary nucleic acids, or a solid environmente.g. an electrophoresis gel sampling for nucleotides on a nucleic acidsequence. The fabrication of a set of parallel nanotraces 115 serves tohomogenize the total response to changes in local environment 123 sincethe total response is the average of the response of each nanotrace 118connected in parallel between the interdigitated finger region of thesource 116 and drain 117 electrodes. Averaging the response over anumber of nanotraces 118 lowers the failure rate of sensor devices 102during fabrication of the multiplex detection array 101. Because eachnanotrace 118 is in direct electrical contact with the interdigitatedfinger region of source 116 and drain 117 electrode, contact resistance124 between the two materials must be kept low. The present embodimentdepicted in FIG. 1 shows a bottom contact approach for forming theelectrical interface between semiconductor nanotrace 118 and theinterdigitated finger region of source 116 and drain 117 electrodes,however, alternate methods which include top contact between theinterdigitated finger region of source 116 and drain 117 electrodes canbe used to make the electrodes. Because semiconductor nanotraces 118 areelectrically continuous with the interdigitated finger region of thesource 116 and drain 117 electrodes that work back to the source 109 anddrain 114 electrode bonding pads through source 103 and drain electrode104 and 104B, the source-to-drain current can be measured externallythrough electrodes that make contact with source 109 and drain 114electrode bonding pads, Electrical continuity from the bonding pads toan electrode is established using common techniques such as wire or bumpbonding of the multiplex detection array 101 chip to an electronicsboard package (not shown in FIG. 1).

Method for Patterning the Base Electrode Structures:

FIGS. 2A-F illustrate the series of fabrication steps for multiplexdetection array 101 in preparation for binding of probe librariesspecific to the type of test being performed. Initially, substrate 107is used as a base for fabricating the array of sensor devices 102, FIG.2A. Suitable materials for substrate 107 include any semiconductor orinsulating wafer such as glass, doped or undoped semiconductors e.g.silicon, or polymers. Substrates such as flexible polymer films or metalfoils may also be used. A series of parallel, individually-addressablegate electrodes 105 are deposited on substrate 107. If substrate 107 issemiconductor or electrically conducting, an insulating layer (not shownin FIG. 2) may be deposited prior to deposition of gate electrode 105 onsubstrate 107 to provide a means to prevent shorting of gate electrodes105 to the substrate. A suitable material for gate electrodes 105 is atie layer of chromium or titanium (˜5 nm) and a gold electrode layer(˜40-100 nm). A suitable means to deposit gate electrode layer 105 isvacuum deposition and a suitable means to subsequently pattern gateelectrodes 105 is standard lithography. In the embodiment illustrated inFIG. 2A, each gate electrode 105 is common to an entire column of sensordevices that are subsequently deposited over gate electrode 105. Eachgate electrode 105 terminates at a gate electrode bonding pad 108 thatare positioned in an area remote from any sensor devices 102, depictedpreviously in FIG. 1, to enable facile connection with an external setof electrodes.

After patterning of gate electrodes 105, gate dielectric layer 106 isdeposited by chemical vapor deposition. The thickness of the gatedielectric layer 106 is a balance between maximizing the field effectfrom gate electrode 105 and preventing electrical breakdown at too highof an electrical field. A suitable material for gate dielectric 106 issilicon dioxide and the thickness preferably ranges between 10 nm and200 nm. The need for gate electrode 105 is dependent on the applicationof the multiplex detection array 101. As an alternative to that depictedin FIG. 2A, the gate electrode may be formed using standard ionimplantation into substrate 107, which is well known in the art. Anotherembodiment might include using the entire substrate 107 as a common gateelectrode. This does not require deposition and patterning of the metalgate electrode 105 although gate dielectric 106 is always deposited.Similarly, in another embodiment, the need for gate electrode 105 mightbe removed altogether as the chemiresistive measurement of sensordevices 102 may occur without preconditioning of the electricalproperties of semiconductor nanotraces 118 using the field from a gateelectrode 105.

The example illustrated in FIG. 2B shows common gate electrode 105positioned below the column of sensor devices 102 created by sensordevices 102A and 102D in multiplex detection array 101. A continuousmetallic layer is deposited over the surface of gate dielectric 106. Theelectrode material is composed of a tie layer (˜5 nm of chromium ortitanium) followed by a gold layer (˜40-100 nm). The electrode materialsmay be deposited by thermal evaporation, electron beam evaporation, orsome suitable other process. After deposition, a photolithographyprocessing step is performed using a standard photoresist layer that isexposed and developed to generate the gold features that composesegments of both the source 103 and drain 104 electrodes. As part of thepattern, the interdigitated finger region for both source 116 and drain117 electrodes are developed in a single layer with source electrodefingers 116 contiguous with the common source electrode 103. Sourceelectrode 103 is also contiguous between the source side of each sensordevice 102 for a given column. For example, the source electrodeconnects sensor devices 102A and 102D, 102B and 102E, and 102C and 102Fin FIG. 2B. Each source electrode 103 terminates at a source electrodebonding pad 109. The source electrodes 103 are parallel with the gateelectrodes 105 and terminate in an area remote from the sensor devices102 in the multiplex detection array 101. The position of the sourceelectrode bonding pads 109 is offset from the gate electrode bondingpads 108 to accommodate the necessary steps to liberate the gatedielectric 106 above the gate electrode bonding pads 108. Removal of aportion of the gate dielectric layer is illustrated as the gateelectrode window 201 in FIG. 2B. Grouping of the source electrodebonding pads 109 in this region provides a means for facile electrodeconnectivity to an external electronic board (not shown).

The interdigitated fingers on the drain side 117 is contiguous with thefirst leg of drain electrode 104 which terminate with the drainelectrode stub bonding pad 110 on each sensor device 102. The drainelectrode stub bonding pad 110 serves as a termination point forsubsequent transfer of the drain electrical connection into a secondaryelectrode plane (described later). In addition to the deposition of theelectrode structures 103 and 104, alignment marks for aligningsubsequent layers are also patterned into the gold electrode layer onthe edges of multiplex detection array 101 that are not visible in FIG.2.

Fabrication of the Semiconductor Nanotraces

After fabrication of the base electrode layers, a semiconducting activelayer is deposited over the entire wafer. Chemical vapor deposition,electron beam deposition or other suitable methods may be employed.Suitable materials for the semiconducting active layer are Group IV,III-V, and II-VI materials including tin oxide (SnO₂), indium oxide(In₂O₃), and zinc oxide (ZnO) and other nitrides and chalcogenides.Using the method of nanoimprint lithography (NIL) and a series of dryetch processes, the semiconducting active layer is patterned into a setof parallel nanotraces 115 over the interdigitated finger region of thesource 116 and drain 117 electrodes. A separate set of parallelnanotraces 115 are patterned over each sensor device 102, FIG. 2C. Eachnanotrace 118 in the set of nanotraces 115 is patterned such that thelong axis of the nanotrace 122 runs parallel with the column of sensordevices 102 and perpendicular with the interdigitated finger region ofthe source 116 and drain 117 of the source 103 and drain 104 electrodes.

Nanoimprint lithography is a special processing technique that enablesnanodimension features to be patterned into the semiconducting activelayer using a top down approach without the use of expensive stepperaligner tools. The dimensions of each semiconductor nanotrace 118 arecritical for increasing the response sensitivity to a level thatprovides practical direct electrical transduction of target moleculebinding. This is achieved because the surface-to-volume ratio of eachsemiconducting nanotrace 118 is large due to the small width 119 anddepth 120 of the nanotrace 118 (FIG. 1 Inset). Using nanoimprintlithography, nanotraces can be patterned with physical geometries thatare comparable to the grain dimensions of the nanotraces 118, making themolecular-semiconductor electronic interaction more pronounced.Nanodimension registration with the interdigitated finger regions of thesource 116 and drain 117 is achieved using a nanoimprint processing toolsuch as Molecular Imprints Imprio 5500 (Austin, Tex.). Also noteworthyis that the distance between the gate electrode and the set of parallelnanotraces 115 is dictated by the thickness of layer 106 and is a known,regular distance for all of the nanotraces 118 in the set of parallelnanotraces 115. This is in contrast to nanowire sensors where thedistance between the active semiconductor nanowire and the electricfield from gate electrode 105 can lead to background inhomogeneities inthe response. The details of the method of nanoimprint lithography aredefined further in the following sections of this description.

Developing the Electrical Architecture for Addressing Each DrainElectrode

After fabrication of the set of parallel semiconducting nanotraces 115over each sensor device 102, the remainder of the drain electrodes 104Bis deposited, FIG. 2D-F. Before addition of the drain electrode layer, aphotoresist layer is spun over the entire surface and patterned, FIG.2D. The pattern includes “islands” of photoresist 202 that are designedto protect the set of parallel nanotraces 115. Source 109 and gate 108electrode bonding pads are also protected during the remainingfabrication steps of multiplex detection array 101 (not shown in FIG.2). Referring to FIG. 2D, an insulating oxide layer 111 (˜50-100 nm) isfirst deposited over the entire wafer to insure that contiguous drainelectrodes 104B are electrically isolated from the underlying layer anddo not electrically short to source electrodes 103. Electricalcontinuity between drain electrode stub bonding pad 110 and the drainelectrode layer 104E is created by first patterning a series of “vias”112 through the oxide insulating layer 111 directly over each drainelectrode stub bonding pad 110. Vias 112 are created using a dry etchprocess with a patterned photoresist layer as the etch stop. Aftercomplete etching of the oxide in the vias 112 is insured, a tie layer(˜5 nm) and gold layer (˜100-200 nm) are deposited over oxide insulatinglayer 111 to a thickness that insures complete filling of vias 112 andelectrical continuity to the drain electrode continuity pad pickup 113in the drain electrode layer 104B. Wet etching of the gold/tie layerslead to the formation of drain electrodes 104B that terminate at drainelectrode bonding pads 114 in an area remote from the sensor devices102. FIG. 2E shows the final drain electrode pattern. Drain electrodes104B are perpendicular to source 103 and gate 105 electrodes in theunderlying layer. Drain electrodes 104B provide electrical continuitybetween all sensor devices 102 in each row. FIG. 2E shows an examplewhere a drain electrode 104B is electrically contiguous between sensordevices forming the row 102A, 102B, 102C and a second drain electrode104B is contiguous across the row containing sensor devices 102D, 102E,102F. Each of the drain electrodes terminates at a separate drainelectrode bonding pad 114 which can be connected to an externalelectrical monitoring device.

Preparing the Final Device for Microfluidic Coupling

As a final measure, oxide protection layer 203 (˜100 nm) is depositedover the entire surface of multiplex detection array 101 as illustratedin FIG. 2F. In order to recover the set of semiconductor nanotraces 115over each sensor device 102 for further biomolecular or chemicalcoupling, final photoepoxy resist layer 204 is spin-coated and patternedover sensor devices 102 to provide a bonding face for a microfluidiccover plate. Photoepoxy resist layer 204 serves two purposes. First,photoepoxy resist layer 204 acts as the etch stop during the oxide dryetch which removes the oxide material back to protection islands 202over the set of parallel nanotraces 115. After patterning of thephotoepoxy resist, a dry etch process is used to remove the silicondioxide from the final oxide protection layer 203 and the oxide layer111 in that order. This produces access windows 205 to thesemiconducting nanotraces 115 over each sensor device 102.

Photoepoxy resist layer 204 also serves as the final bonding andinterface layer that makes contact to the microfluidic cover plate(described later). After the dry etch of the oxide layers is completeover protection islands 202, and protection islands 202 are strippedfrom the surface of the set of parallel semiconductor nanotraces 115, alight piranha etch (1 part 30% H₂O₂: 3 parts concentrated H₂SO₄) removesany residual organic residue from the surface of the set ofsemiconductor nanotraces 115 yielding a pristine semiconductor surfacefor covalent attachment of probe molecules. As a final measure,multiplex detection device 101 is treated with an oxygen ashing step10-30 minutes at a pressure of 700 mTorr at a power of 300 W with O₂flow of 8 sccm. Oxygen ashing leads to diffusion of O⁻ into the bulklattice of the semiconducting nanotrace 118 surface and completes thestoichiometric ratios necessary to convert the nanotraces 118 into asuitable material for molecule coupling and direct electricaltransduction. Oxygen ashing is carried out using an instrument such as aMarch Asher and is preceded by a thermal annealing step (10 min. at 200°C.) in ambient.

Detailed Description of the Method of Nanoimprint Lithography

Fabrication of the set of parallel semiconductor nanotraces 115 is oneof the core features of multiplex detection array 101. To fabricate theset of parallel nanotraces 115, the method of Nanoimprint Lithography(NIL) is employed. NIL was first described in the prior art by U.S. Pat.No. 6,334,960, which is hereby incorporated by reference herein. FIGS.3A-E illustrate the process for preparing the nanoimprint features intothe active semiconducting layer. The first step is to fabricate imprinttemplate 301 that is a separate component to multiplex detection array101. Template 301 is composed of a quartz wafer that has been previouslypatterned using electron beam lithography. The method for making theimprint template is described in the prior art by U.S. Pat. No.6,334,960. Briefly, the electron beam writes individual features into ane-beam photoresist which after development appears as grooves in theresist. The pattern is transferred into a thin chromium layer ˜30 nmthick using a dry etch process. The chromium layer is then used as ahard etch stop during a dry etch of the quartz wafer. The e-beam writtenfeatures appear as “grooves” 302 in quartz template 301 with the desiredpattern. The chromium layer is stripped leaving a transparent,nanopatterned quartz template 301 as a free-standing wafer. Quartztemplate 301 is shown above multiplex detection array 101 wafer in FIG.3A. For reference, the fabrication step of multiplex detection array 101captured in FIG. 3A is that previously illustrated in FIG. 2B. As afinal measure, self-assembled “release” monolayer 303 is applied to thesurface of template 301 by immersing template 301 into solutionovernight followed by rinsing of excess. The fabrication of quartztemplate 301 is considered the “slow” step. Once fabricated, it can beused to make many copies of the nanoimprint pattern. FIGS. 3B-E show across-sectional view of the processing steps for preparing the set ofparallel semiconductor nanotraces 115 using template 301. Template 301is a full wafer which contains multiple copies of multiplex detectiondevice 101, referred herein as the “die”. The design of multiplexdetection device 101 is created such that all of the sets of parallelnanotraces 115 for every sensor device 102 in a multiplex detectionarray 101, and all copies, or dies of the multiplex detection array 101are fabricated during a single NIL process. However, FIGS. 3A-Eillustrates a cross-sectional view of the NIL process sequence thatoccurs over only a single sensor device 102 in one of the multiplexdetection device 101 dies.

Initially, quartz template 301 is positioned such that grooves 302 areregistered over the interdigitated finger region of the sensor devices102. As illustrated previously in FIG. 2C, the parallel set ofsemiconductor nanotraces 115 is perpendicular to interdigitated fingerregion of the source 116 and drain 117 portions of the electrodesspanning the distance therebetween. A hard mask or back anti-reflectioncoating (BARC) layer 304 (˜60 nm) is deposited onto the device layerstack which, in this cross-section, consists of semiconductor activelayer 305 (˜20-100 nm) on gate dielectric 106 (˜20-100 nm) which is ongate electrode 105 (˜40 nm) and supported by substrate wafer 107 (˜500um). The cross-section view in FIGS. 3A-E represents a view that isparallel to interdigitated finger regions of the source 116 and drain117 electrodes, but is in the space between adjacent source 116 anddrain 117 fingers so they do not appear in this cross-sectional view.

After BARC layer 304 is spun cast onto the device stack, photoresistdispenser 306 places droplets of SFIL or other suitable nanoimprintphotoresist 307 onto BARC layer 304 which spreads into a continuous thinlayer 308 onto the surface. Referring to FIG. 3C, template 301 isbrought into contact with photoresist 308. Template 301 is angled ontolayer 304, so as to create a wave front of photoresist 308. This wavefront expels gas pockets, resulting in complete filling of grooves 302of template 301. Referring to FIG. 3D, ultraviolet light rays 309 (˜300W/cm², 20 s) expose photoresist 308 through template 301. Photoresist308 reacts and polymerizes into rigid imprint layer 310. After exposure,template 301 is moved from the surface, leaving hard imprint layer 310which have sharp imprint features 311 that are the negative of grooves302 in template 301. The remaining area is a thin residual layer 312between raised imprinted features 311. Template 301 is released fromhard imprint layer 310 under the assistance of release layer 303 ontemplate 301, FIG. 3E.

After hard imprint features 311 are formed, the features are“transferred” into semiconductor active layer 305 using a series of dryetch processes, FIGS. 4A-D. As a first step (FIG. 4A), a plasma dry etchsystem such as an Oxford Plasma Lab 80 RIE operating under a CHF₃:O₂environment (15 sccm CHF₃, 7.5 sccm O₂, p=25 mTorr) and a DC bias of˜200 V was used to remove the residual silicon-containing SFIL polymerlayer 312 at an etch rate of ˜30-40 nm/min. (˜50 s). A slight over-etchis used at this stage. This etch decreases the height of hard imprintfeatures 311 while simultaneously removing residual layer 312. The neteffect of this etch is to reveal the surface of the BARC (organic) layer304. The next process is transfer of the pattern into the BARC layerusing an organic dry etch of 100% O₂ (8 sccm, p=5 mTorr) and a DC biasof ˜200 V at an etch rate of 20-30 nm/min. (˜2 min. 15 s). Thedifferential etch rate of the silicon-containing hard imprint layer 311provides a means to selectively etch the BARC (organic) layer to thesurface of semiconductor active layer 305. The BARC layer 304 is used tosmooth out small surface roughness in the wafer and make the final etchinto the semiconductor active layer 305 more uniform. The geometry ofthe etched BARC features 401 under the hard imprint layer 311 is shownin FIG. 4C.

Referring to FIG. 4D, a final plasma etch step consisting of an Ar:Cl₂gas mixture (24 sccm Ar, 6 sccm Cl₂, p=80 mTorr) at a bias of ˜200 V,and an etch rate of 10-15 nm/min. (˜1-3 mins. depending on the thicknessof semiconductor active layer 305) is used to remove semiconductoractive layer 305 and yield the set of parallel nanotraces 115. Eachsemiconductor nanotrace 118 has the width 119, depth 120, and spacing121 defined previously in FIG. 2C. Alternatively, a hard mask layer, forexample chromium, can be used if necessary to achieve the selectivelyand aspect ratio desired for semiconductor nanotraces 118. As a finalstep, FIG. 4E, etched hard imprint features 311 and etched BARC features401 are removed using a piranha wet etch process. This process cleansthe surface of semiconductor nanotraces 118 and prepares them forcovalent attachment of probe molecules in later steps.

FIG. 5 illustrates a High-Resolution Scanning Electron Microscope(HRSEM) cross-section micrograph of the process step just afternanoimprinting of the hard imprint features 311 over an example sensordevice 102 (FIG. 1) in multiplex detection array 101. The photomicrographs are illustrative of the fabrication state depicted in FIG.4A where base substrate 107, a p-doped silicon wafer (˜500 μm) forexample, is serving as gate electrode 105. A silicon dioxide layer (˜100nm) serves as gate dielectric 106 upon which the active semiconductor,SnO₂ layer 305 in this embodiment, is deposited (˜70 nm). A backanti-reflection layer 304, Transpin™, is deposited on semiconductoractive layer 305, upon which final SFIL layer 308 is deposited andpatterned with the alternating regions of raised hard imprint features311 (˜150-300 in) and the thin residual layer 312 (˜20-80 nm). Width 501and spacing 502 of hard imprint features 311 are equal to the finaldesired width 119 and depth 120 of the individual semiconductornanotraces 118.

FIG. 6A illustrates a HRSEM photomicrograph after the breakthrough etchof the BARC layer 304 to semiconductor active layer 305 (example of etchstate represented by FIG. 4C). Access of the reactant gases to thesurface of semiconductor 305 is illustrated as 601 in the figure.Additionally, residual organic debris 602 can be seen and the bestresults occur when the dry etch of BARC layer 304 is carried out tocompletion to remove these features. FIG. 6B illustrates the processafter completion of the dry etch of semiconductor active layer 305 andstripping of the etched BARC layer 304 and etched hard imprint layer 311(example of state in FIG. 4E). The embodiment of semiconductornanotraces 118 illustrated in FIG. 6B includes a semiconductornanotraces design with bridging segments 603 between each semiconductornanotrace 118 in the set of parallel semiconductor nanotraces 115. Whilethe semiconductor nanotrace “mesh” embodiment is slightly altered fromthe previous illustration, ultimately the individual nanotraces 118possess the same width 119 and spacing 120 of original hard imprintfeatures 312. The pattern is simply altered by selection of a differentdesign written into the template 301. After the process depicted in FIG.6B is completed and the set of parallel nanotraces 115 are formed andcleaned free of organics, the multiplex detection array 101 is ready fordeposition of the anchor probe library.

Synthesis of Anchor Probe Libraries on the Surface of the ActiveSemiconductor Nanotraces

After fabrication of the electrical architecture of the multiplexdetection device 101 illustrated previously in FIG. 2, the set ofparallel semiconductor nanotraces 115 for each sensor device 102 isfunctionalized with a sensitizing compound. FIGS. 7A-C illustrate thesteps for coupling the sensitizing compounds onto the surface of theparallel set of semiconductor nanotraces 115. Generally, each of thesemiconductor nanotraces 118 within each parallel set of semiconductornanotraces 115 receives the same sensitizing compound. In contrast, eachparallel set of semiconductor nanotraces 115 on different sensor devices102 receives a different sensitizing compound making it uniquelyresponsive to external targets relative to neighboring sensor devices102 in the multiplex detection array 101. The collection of all thesensitizing compounds for a given multiplex detection device 101 iscalled the library. Different sensitization compounds from the libraryare added to each sensor device 102 by partitioning the sensor devices102 into different reaction wells during coupling. Methods to segregatethe different sensor devices 102 on multiplex detection device 101during coupling of the sensitization compounds is described later.

Generally, the sensitizing compounds consist of “probe” molecules thatare covalently attached to the surface of the semiconductor nanotraces118. The probes have specific affinity for different targets. Methodsthat provide a means for parallel deposition of each anchored probe inthe library onto the respective sets of parallel semiconductornanotraces 115 and all of the sensor devices 102 in the multiplexdetection array 101 during a single process is preferred. Generally, thespecific anchored probes that are selected to be in the library of agiven multiplex test are chosen based on known outcomes from individualsensor device and are representative of the type of test that is beingperformed. This simplest case consists of a single sensor device 102that responds to a single or a plurality of specific targets.

In the preferred embodiment described in FIG. 7, the probe molecules inthe compound library are nucleic acid sequences that are designed torespond very specifically to the binding of the complementary sequence.In other embodiments, the anchored probes could be proteins that responddifferentially when the binding of different antibodies occur.Similarly, polymers or other macromolecules that exclude or specificallybind different solution analytes or gas phase analytes can be used asthe sensitizing compound which makes the sensor device 102 unique. Inthe embodiment where the probe library consists of short nucleic acidsequences (oligonucleotides), individual oligonucleotides can besynthesized directly from the surface of the semiconductor nanotraces118. A plurality of oligonucleotides can be synthesized onto theparallel set of semiconductor nanotraces on each sensor device usingsuitable methods such as PhotoGenerated Reagent (PGR) described in theprior art in U.S. Pat. No. 6,965,040, which is hereby incorporated byreference in its entirety. The method to deposit an anchor probe libraryof oligonucleotides using the method of PGR is illustrated in FIG. 7A-Cand described below.

Initially, multiplex detection device 101, illustrated previously inFIG. 2F, is enclosed with microfluidic coverplate 701, FIG. 7A.Microfluidic plate 701 consists of a series of fluidic wells 702 (˜15 umin depth) that are connected by a network of fluidic channels 703 (−90um in depth) that work back to a single entrance and exit port (notshown) where fluidic coupling is made externally to a fluid manifold.The fluidic network consists of both parallel and serial connections ofindividual fluid wells 702 via fluidic network of channels 703.Microfluidic cover plate 701 can be glass or other suitable moldedplastic component that provides a leak-tight seal between fluid wells702. Additionally, the fluidic cover plate wafer must be transparent tosupport photoactivation of certain reagents during optical irradiationusing the method of PGR. Each microfluidic well 702 is designed to fullyenclose a single sensor device 102 in multiplex detection array 101.Each microfluidic well 702 provides a reaction center wherephotogenerated acid can diffuse throughout, but cannot cross intoneighboring microfluidic wells 702. While synthesis of nucleic acidanchor probes is illustrated as the preferred embodiment in FIGS. 7A-C,other probe-specific classes such as proteins, small metabolites,nanoparticles, polymer nanospheres and other receptors for gas phasestargets can also be deposited, or synthesized, depending on theapplication. Additionally, some of the sensor devices 102 in multiplexdetection array 101 can be employed as references and controls. Thesesensor devices 102 would receive special sensitization compounds thatmay exclude, trap, or permit only a specific entity in the environmentsurrounding the semiconductor nanotraces 118. Likewise, sensor devices102 may be designed to bind known sequences spiked into the samplesolution, for example, as a positive control.

FIG. 7B illustrates the state of the multiplex detection array 101 aftercompletion of the method of PGR. At this point, the microfluidic coverplate 702 is removed and the net result is a multiplex detection array101 where the set of parallel nanotraces 115 on each sensor device 102has a unique anchor probe molecule 704 synthesized on the surface of allof the semiconductor nanotraces 118 in the set of parallel nanotraces115. FIG. 7B inset (i) illustrates that a plurality of copies of thesame anchor probe oligonucleotide molecule 704 are synthesized from thesurface of semiconductor nanotrace 118 and are limited only by themolecular packing density of the anchor probe molecules 704. At the endof the PGR process, the semiconductor nanotraces 118 for each sensordevice 102 possess anchor probe molecules 704 covalently coupled to thesurface where, in this example, the anchor probe sequence 705 is uniqueto a single sensor device 102. The unique anchor probe sequence 705,FIG. 7B(ii) for each sensor device 102 is dictated exclusively by thefluidic confinement of the PGR reagents within each microfluidic well702 that enshroud the set of semiconductor nanotraces 115 on each sensordevice 102. The number of different or redundant anchor probes 704 inthe multiplex detection array 101 library is limited only by the numberof sensor devices 102 and corresponding microfluidic wells 702 designedin the microfluidic cover plate 701.

As a final measure, multiplex detection array 101 with anchored probes704 is packaged onto electronics board 706, FIG. 7C. Electrode bondingpads on multiplex detection device 101 are made contiguous with theelectronics board 706 using a suitable technique such as wire or bumpbonding. In the embodiment shown in FIG. 7C, a wire bond 707 connectionis made between gate electrode bonding pad 108 and gate electronicscontrol lead 708. Additionally, wire bond 709 between the sourceelectrode bonding pad 109 and source electronics control lead 710, andwire bond 711 between the drain electrode bonding pad 114 and drainelectronics control lead 712 are made. Some level of embedded logic isalso included on the electronics board 706 (not shown) that enablesmultiplex signal acquisition, processing and results determination.

Detection of the Target Molecules

In the case of the preferred embodiment described above, the multiplexdetection array 101 would be packaged within a common fluidic-tightvessel (not shown) that serves as the sample fluid reaction chamberwhich brings together the sample fluid with the multiplex detectionarray 101. For example, in the case of a diagnostic test for a virulentpathogen, the target nucleic acid sequence would bind with itscomplementary anchored probe oligonucleotide sequence 705 on one of thesensor devices 102 in the multiplex detection array 101. The sensordevice 102 that bears the matching anchored probe oligonucleotidesequence 705 that is complementary to the target would incur a change inthe source-drain electrical current which would be measured in theexternal circuit. A temperature controller device can be used to insurethat the conditions for optimum binding affinity are achieved duringreaction. A solid state cooler/heater device such as a thermoelectriccooler, for example, may be used in the instrument and pushed up againstthe cartridge when it is inserted into the instrument. Signal processingfrom the embedded control logic would then indicate to the user that thepresence of the target nucleic acid sequence corresponding to a matchwith the known anchor probe sequence 705 was present in the sample. Theresult would be displayed on a digital display device that is part ofthe analysis instrument. The user would then determine a course ofaction based on the result of the diagnostic test. In the simplest case,a single sensor device 102 is used to determine the identity of anunknown target. The multiplex detection array 101 is designed to assessthe presence of a single or plurality of targets during a single sampleintroduction onto multiplex detection array 101. The embedded controllogic makes a continuous measurement of the current in all of thesensor, reference and control devices 102 in the multiplex detectionarray 101.

In alternate embodiments, the anchored probe oligonucleotide would bedesigned to look for a specific sequence that had been expressed such asRNA, or DNA that is specific to a particular organism. In otherembodiments, the anchor probes may be nucleic acid sequences that havebeen selected based on a specific affinity to a target molecule orentity on a surface, e.g. a cell wherein the anchored probe sequencecoils into a 3D conformation that interacts with the target in the formof an aptamer. In another embodiment, the anchor probe molecule may be aprotein that has a specific affinity for a target protein or antigen, orthe anchor probe molecule may be a small molecule that has a specificaffinity for another molecule or ion in solution.

FIG. 8A-B illustrates the chemical binding effect of targets to theanchor probe molecules 704 on multiplex detection array 101. In thisembodiment, anchor probes 704 synthesized on the surface ofsemiconductor nanotraces 118 display a baseline current 801 that ismeasured and recorded prior to introduction of target molecules 802,FIG. 8B. Upon addition of target molecule 802 to the fluid space abovesensor device 102 (FIG. 8B), and if the target sequence 802 matches theanchor probe sequence 705 on any given sensor device 102 in themultiplex detection array 101, it will hybridize with the surfacecomplement. Upon hybridization, the current traveling through thesemiconductor nanotrace 118 will change at the point indicated by 803.Because anchor probe sequence 705 of sensor device 102 that undergoes achange in current is known, the identity of the unknown target sequence802 can be made. The change in the current will be a new value 804 thatindicates the presence of target 802. The magnitude and direction of thechange in current is indicative of the concentration of target, natureof the surface interaction, local electric field and properties of thesemiconductor nanotraces. The properties of the semiconductor nanotracescan be influenced by the doping level, external field applied by thegate electrode and other things that can affect or change the majoritycarrier concentration and mobility.

Although the present invention has been described with reference tospecific details, it is not intended that such details should beregarded as limitations of the scope of the invention, except as and tothe extent that they are included in the accompanying claims.

The invention claimed is:
 1. A method for making an array of semiconductor nanotraces, comprising: (a) supplying a substrate; (b) forming a series of individually-addressable electrodes having bonding pads on the substrate using standard lithography; (c) depositing a layer of a semiconductor; and (d) using nanoimprint lithography (NIL) and dry etches to form a set of parallel nanotraces of the semiconductor between the electrodes.
 2. The method of claim 1 further comprising depositing a dielectric layer before step (b).
 3. The method of claim 2 further comprising depositing a gate electrode before depositing the dielectric layer such as to form a field effect transistor.
 4. The method of claim 1 wherein the step of using NIL comprises: (a) applying a layer of organic material; (b) applying drops of polymerizable material; (c) contacting the polymerizable layer with a template having nanodimension depressions so as to cause the polymerizable material to flow into the depressions; (d) applying ultraviolet radiation to form polymerized material; (e) removing the template to leave raised features of the polymerized material that flowed into the depressions; (f) etching the polymerized and organic material; (g) etching the semiconductor; and (h) removing the remaining polymerized and organic material.
 5. The method of claim 4 where the organic layer is a back anti-reflection coating.
 6. The method of claim 4 wherein the organic layer is removed using a dry etch process with oxygen gas as the etchant.
 7. The method of claim 4 wherein the polymerizable imprint layer is removed using a dry etch process with a mixture of a partially fluorinated hydrocarbon gas and oxygen.
 8. The method of claim 4 where the semiconductor layer is removed using a dry etch process with a mixture of argon and chlorine.
 9. The method of claim 4 where the polymerizable layer and the organic layer are stripped after transfer of the pattern into the semiconductor using a piranha wet etch.
 10. The method of claim 1 wherein the substrate comprises doped silicon.
 11. The method of claim 1 wherein the semiconductor layer is deposited using electron beam or vacuum evaporation.
 12. The method of claim 1 wherein the semiconductor layer is deposited using molecular beam epitaxy, electron beam evaporation, or chemical vapor deposition.
 13. The method of claim 1 wherein the semiconductor layer is deposited by spin casting.
 14. The method of claim 1 wherein the semiconductor layer is deposited by sputter deposition.
 15. The method of claim 1 wherein the semiconductor layer is annealed in different environments to condition the stoichiometry for the optimum electronic properties for sensing.
 16. A method for making a multiplex array detection device, comprising: (a) supplying a substrate; (b) forming a series of individually-addressable electrodes having bonding pads on the substrate using standard lithography; (c) depositing a layer of semiconductor; (d) using nanoimprint lithography (NIL) and dry etches to form a set of parallel nanotraces of the semiconductor between the electrodes; (e) synthesizing selected anchor probe molecules on the semiconductor nanotraces; and (f) packaging the array onto an electronics board.
 17. The method of claim 16 wherein the anchor probe molecules are synthesized by enclosing the semiconductor nanotraces in a microfluidic coverplate and using the method of Photo-Generated Reagent. 